Typically, polyurethane-polyisocyanurate (PUR-/PIR) rigid foams are produced by reacting a polyol- with an isocyanate component in the presence of a propellant. Furthermore, additives such as foam stabilisers and flame retardants can be added. Compared with other rigid foams such as PUR rigid foams, PUR-PIR rigid foams have excellent thermal stability and improved flammability properties. The cause of these improved properties is ascribed to isocyanurate structural elements.
For economic reasons, it is worth trying to use inexpensive raw materials as far as possible. In terms of the isocyanate-reactive component of a PUR/PIR rigid foam formulation, this means, for example, the use of inherently inexpensive production residues in which it is a basic prerequisite that hydroxyl groups are present or can be produced. The attempt to achieve improved sustainability should also be mentioned as a further aspect of the use of such production residues. The adaptation of production residues to expensive PUR-/PIR rigid foams avoids them being disposed of, such as by incineration, thereby conserving the environment and contributing to the reduction in the use of inherently scarce raw materials, and ultimately of crude oil.
A production residue of this type occurs in the distillation residue when Bisphenol A is produced. Raw Bisphenol A (BPA) is processed by purifying the reaction product of acetone and phenol by distillation, wherein so-called BPA resin occurs as a distillation residue. Depending on the intensity of this distillation process, this type of BPA resin can still have considerable proportions of an 4,4′-isopropylidenediphenol, e.g. 10 to 60% w/w. The remaining proportions are distributed amongst other structural elements derived from phenol, acetone and Bisphenol A, such as the 2,4′- and 2,2′ isomers of the bisphenol base body. An example of a composition is described in KR 2002 0065658 A. There can be a considerable number of deviations from this in individual cases. Regardless of this, within the scope of the present application, the term BPA resin comprises substantially all distillation residues of Bisphenol A production processes.
Moreover, the consistency of the BPA resin also depends on the distillation process. While the melting point of the Bisphenol A (approx. 155° C.) is normally not close to being reached, nevertheless the softening point of the BPA resin still remains so high that there is no question of its direct use as an isocyanate-reactive component for this reason alone. For example, BPA resins soften between 70 and 100° C.; however, they are able to flow only at higher temperatures. It might be mentioned, furthermore, that the phenolic hydroxyl groups, when present in the BPA resin, are not generally suitable for the synthesis of polyurethanes, and particularly not if good long-term application properties are needed, in particular at an elevated temperature. Urethane groups based on phenolic hydroxyl groups qualify as thermolabile.
It is a task, therefore, of the present invention to produce a method for producing polyurethane-polyisocyanurate rigid foams using cost-effective polyols based on hydroxyl-functional residues from the production of Bisphenol A.
Within the meaning of this application, polyurethane-polyisocyanurate (PUR/PIR) rigid foams are characterised in that isocyanate groups are used in excess compared with isocyanate-reactive groups, so that both urethane groups are formed, as well as isocyanurate structural elements due to isocyanate-trimerisation reactions, and possibly urea groups from the reaction with water.
Besides urethane groups, urea groups and isocyanurate structures, the PUR/PIR rigid foams may even contain other groups, such those appearing by the reaction of the isocyanate group with other groups as well as with hydroxyl groups or other isocyanate groups. The reaction of the isocyanate group with urea groups results, for example, in biuret structures, similarly containing allophanate structures by the reaction of isocyanate groups with urethane groups. These structures are then present in the polymer together with the urethane-, urea- and isocyanurate groups.
Furthermore, the invention concerns the PUR/PIR rigid foams obtained in this manner as well as the use of the polyol mixtures producible in accordance with the inventive method in the production of PUR/PIR rigid foam with suitable surface layers.
The composite elements obtained in this manner and producible using conventional machines form a further subject matter of the invention.
Other subject matters of the invention are derivatives of the BPA resin which flow at room temperature and which are produced by alkoxylation, as well as a method for their production.
The alkoxylation of Bisphenol A itself is known (Mihail Ionescu in Chemistry and Technology of Polyols for Polyurethanes, Rapra Technology Limited, Shawbury, Shrewsbury, Shropshire, SY4 4NR, United Kingdom, 2005, pp. 403 ff), wherein three methods are described:                1.) Alkoxylation of Bisphenol A (with ethylene oxide (EO) or propylene oxide (PO)) as a suspension in an inert solvent at 90 to 120° C. in the presence of a basic catalyst, in particular in the presence of tertiary amines.        2.) alkoxylation of Bisphenol A as a suspension in liquid PO in the presence of a tertiary amine as a catalyst, wherein, after approx. 2 hours while stirring at 90 to 100° C., EO is added in a second step.        3.) Alkoxylation of Bisphenol A as an approx. 50% suspension in a separately made reaction product in the presence of a tertiary amine as a catalyst.        
It is generally disadvantageous in these three methods to use the comparatively expensive Bisphenol A, as well as the technically challenging reaction as a suspension which always carries the risk of undesired sediments. It is a particular disadvantage in Method 1 to use an inert solvent which, on the one hand, limits the space-time-yield, and on the other hand, has to be separated expensively. From a process reliability standpoint, alternative Method 2 is classified as critical because a consequence of the reaction, if, for instance, the reactor cooling fails, can result in the significant adiabatic heating of the reacting mixture, thereby even triggering the exothermic decomposition of the contents of the reactor. A particular disadvantage of Method 3 is the use of the reaction product as a suspension agent which also affects the space-time-yield negatively.
A task of the present invention is also to overcome these disadvantages.
In the state of the art cited above, Ionescu described the possibility of using pure alkoxylated Bisphenol A as a starter for the production of urethane-isocyanurate foams. However, our own studies show that the flammability behaviour of PUR-/PIR foams based on pure ethoxylated Bisphenol A is not satisfactory (see also examples A1.5 in Table 1 and B1.7 in Table 3).
KR 2002 0065658 A describes the use of a BPA resin as a starter for the KOH-catalysed reaction exclusively with propylene oxide, wherein polyol mixtures with hydroxyl values of 300 to 500 mg KOH/g and with viscosities at 25° C. of 1500 to 4000 cps (cps corresponds to mPas) are obtained. Furthermore, the conversion the polyol mixtures to polyurethane (PUR) rigid foam is mentioned. The use for PUR/PIR rigid foams is not described.
Polyether, which is based on propylene oxide, has predominantly secondary hydroxyl end groups. Polyol components for PUR/PIR foams, whether they are polyether- or polyester polyols, should preferably have primary OH end groups however. The propoxylated BPA resin described in KR 2002 0065658 is therefore not particularly well suited for the production of PUR/PIR foams.